The long-term aim is to understand at a concrete level the nature and biological properties of positional memory. The broad objectives are 1) to consolidate our knowledge of biological aspects of the in vitro and in vivo assay system that has been devised so that there will be a firm basis for future experiments on molecular properties of positional memory, and 2) to identify anteroposterior positional markers for avian wing mesodermal cells. At present the assay consists of grafting fresh or cultured, intact or dissociated anterior mesoderm from quail wing buds into posterior slits in host chick wing buds. The formation of supernumerary cartilage is the specific endpoint for the experiment. Specific experiments involve determining the cellular composition of the supernumerary cartilage formed in these experiments; determining whether or not the synthesis of type II collagen can be repressed in orthotopically grafted, cultured quail mesoderm; determining if positional memory will be maintained in cells kept dissociated in culture; determining whether premuscle mesodermal cells can participate in the formation of supernumerary cartilage; determining if postional memory can be demonstrated in older wing mesoderm; examining the nature of the response when mixtures of anterior and posterior cells are grafted into host wing buds; and the effect of retinoic acid on positional values of wingbud mesodermal cells. Methodology involved includes in vivo grafting; cell dissociation; in vitro culture of cells and tissues; morphological methods ranging from scanning and transmission electron microscopy, to histology, to gross skeletal stains; immunocytochemistry; monoclonal antibody production.